You can also look at the binding nature of the harmones sex kicks off, and the fact that pre-marital sex is disproportionately cruel to women compared to men.
The main harmone that I know of is oxytocin, which is called the “love harmone”. It’s the same harmone produced is lesser quantities when we smile at a loved one, and it’s also prominent in breastfeeding, to help a mother bond with her new child. Sex literally creates a harmonal and emotional bond between people. Bonding yourself to someone with harmones isn’t a good basis for a relationship, I would say. Better to be willing to commit and bond yourself without them, and then add the harmones in to strengthen that bond.
As for harm to women - women are affected far wose by many STDs, as the sexual act is far more internal to their bodies and therefore the diseases are closer to places where they can do significant damage, resulting in higher rates of sterility or STD-related cancers.
Further, the main consequence of sex - children - ends up being primarily the woman’s burden, whether she has an abortion, adopts, or chooses motherhood. First, there is the fact that she must make this choice at all, and the likelihood that she will be pressured to abort by an unprepared father. Note that pregnancy is likely to end the relationship no matter what the woman chooses, but especially if she chooses abortion, and note also that the woman will be at greater risk for mental and physical illnesses after birth, miscarriage, or abortion if she becomes pregnant without sufficient support from her partner. Sex only within marriage means that the woman has at least some greater legal guarantee of responsibility from her partner if she becomes pregnant. She is less likely to be unsupported emotionally and physically. Note also that actual use birth control effectiveness rates are often lower than 90%, meaning that every year a sexually active woman has a 1-in-10 chance of getting pregnant even with birth control. Imagine how that adds up over 5 years, or 10 (there are stats on this, but I don’t have time to dig them out). That means a woman engaging in premarital sex actually has a very significant chance of struggling with the difficulties described in this paragraph.
Therefore, pre-marital sex is clearly anti-feminist.
Note: I am using solely secular arguments here, and am not actually intending to promote abortion or contraception; however, they are relevant realities that are pertinent to discussions of pre-marital sex.